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參數資料
| 型號： | LMV248LQX |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 通信及網絡 |
| 英文描述： | Electrical Tape; Peak Reflow Compatible (260 C):No RoHS Compliant: Yes |
| 中文描述： | SPECIALTY TELECOM CIRCUIT, CQCC16 |
| 封裝： | 4 X 4 MM, 0.80 MM HEIGHT, LLP-16 |
| 文件頁數： | 9/11頁 |
| 文件大?。?/td> | 289K |
| 代理商： | LMV248LQX |
Application Section
(Continued)
The LMV248 has separate inputs for the coupler/detector
feedback signal(s). These may be combined as a single
input when using a single coupler/detector that accommo-
dates both RF bands. When the two are combined as shown
in Figure 5 internal current sources are placed in parallel. To
maintain correct temperature compensation characteristics
for the applications circuit, an external biasing resistor, R'
should be added externally. For this arrangement, VfA, VfB,
and TC all are returned to a common supply, V
CC
.
Selecting Coupler/Detector
Coupler Calculations:
The applied Ramp voltage controls the RF power output.
Because of this the maximum Ramp voltage sets the mini-
mum attenuation that is allowed in the direction coupler used
to sense output power.
The basic equation is;
P
O
= V
rms2
/R
O
For peak detection it is;
The coupling factor, at maximum power, is defined as C
f
or,
Cf = (V
)
2
/2 x (P
outmax
x R
O
) for couplers that sense
peak power
The limit conditions for the maximum ramp and max power
out is,
V
rampmax
= 2.0V
P
outmax
= 2Watts
R
O
= 50
C
fdB
= 10 x log
10
[(1/2)(V
rampmax
)2/P
outmax
x R
O
)]
C
fdB
= 16.98dB
Attenuation in the directional coupler should be at least
17dB, to assure maximum power out.
General Device Equations
Calculation:
Let Vf be VfA or VfB as selected by BS. Let RVf be the
external series resistance from Vf to the Detector diode.
Voltage at the non-inverting terminal of A1 V
NI
= TC, since
current into A2’s input is small.
Voltage at the inverting terminal of A1 V
INV
= Vf -
[Ramp/(20k
)] x (RVf + 48.5k
)
Assuming the external series resistance for VfA and VfB is
<<
48.5k
:
Voltage at the inverting terminal of A1 V
INV
= Vf – 2.42 x
Ramp
Differential voltage at A1 inputs = V
NI
- V
INV
= TC - (Vf - 2.42
x Ramp) = 2.42 x Ramp - (Vf - TC).
Closed loop regulation of RF output power will force the
average differential voltage at A1 inputs to approach zero:
Average
Including the V
ramp
deadband and the device offset voltage,
the equation for the VfA, B vs. V
ramp
relationship becomes:
VfA, B = 2.42 x (V
ramp
-200mV) + TC - 80mV, all variables
being ground referenced DC voltages.
L
www.national.com
9
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